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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Compact Muon Solenoid | 1/5 | https://en.wikipedia.org/wiki/Compact_Muon_Solenoid | reference | science, encyclopedia | 2026-05-05T13:03:00.987311+00:00 | kb-cron |
The Compact Muon Solenoid (CMS) experiment is one of two large general-purpose particle physics detectors built on the Large Hadron Collider (LHC) at CERN in Switzerland and France. The goal of the CMS experiment is to investigate a wide range of physics, including the search for the Higgs boson, extra dimensions, and particles that could make up dark matter. CMS is 21 metres long, 15 m in diameter, and weighs about 14,000 tonnes. Over 4,000 people, representing 206 scientific institutes and 47 countries, form the CMS collaboration who built and now operate the detector. It is located in a cavern at Cessy in France, just across the border from Geneva. In July 2012, along with ATLAS, CMS tentatively discovered the Higgs boson. By March 2013 its existence was confirmed. Gautier Hamel de Monchenault is the spokesperson for the CMS collaboration since 2024.
== Background == Recent collider experiments such as the now-dismantled Large Electron-Positron Collider and the newly renovated Large Hadron Collider (LHC) at CERN, as well as the (as of October 2011) recently closed Tevatron at Fermilab have provided remarkable insights into, and precision tests of, the Standard Model of Particle Physics. A principal achievement of these experiments (specifically of the LHC) is the discovery of a particle consistent with the Standard Model Higgs boson, the particle resulting from the Higgs mechanism, which provides an explanation for the masses of elementary particles. However, there are still many questions that future collider experiments hope to answer. These include uncertainties in the mathematical behaviour of the Standard Model at high energies, tests of proposed theories of dark matter (including supersymmetry), and the reasons for the imbalance of matter and antimatter observed in the Universe.
== Physics goals ==
The main goals of the experiment are:
to explore physics at the TeV scale to further study the properties of the Higgs boson, already discovered by CMS and ATLAS to look for evidence of physics beyond the standard model, such as supersymmetry, or extra dimensions to study aspects of heavy ion collisions. The ATLAS experiment, at the other side of the LHC ring is designed with similar goals in mind, and the two experiments are designed to complement each other both to extend reach and to provide corroboration of findings. CMS and ATLAS uses different technical solutions and design of its detector magnet system to achieve the goals.
== Detector summary == CMS is designed as a general-purpose detector, capable of studying many aspects of proton collisions at 0.9–13.6 TeV, the center-of-mass energy of the LHC particle accelerator. The CMS detector is built around a huge solenoid magnet. This takes the form of a cylindrical coil of superconducting cable that generates a magnetic field of 4 tesla, about 100 000 times that of the Earth. The magnetic field is confined by a steel 'yoke' that forms the bulk of the detector's weight at 12,500 t. An unusual feature of the CMS detector is that instead of being built in-situ underground, like the other giant detectors of the LHC experiments, it was constructed on the surface, before being lowered underground in 15 sections and reassembled. It contains subsystems which are designed to measure the energy and momentum of photons, electrons, muons, and other products of the collisions. The innermost layer is a silicon-based tracker. Surrounding it is a scintillating crystal electromagnetic calorimeter, which is itself surrounded with a sampling calorimeter for hadrons. The tracker and the calorimetry are compact enough to fit inside the CMS solenoid, which generates a powerful magnetic field of 3.8 T. Outside the magnet are the large muon detectors, which are inside the return yoke of the magnet.
== CMS by layers == For full technical details about the CMS detector, please see the Technical Design Report.
=== The interaction point === This is the point in the centre of the detector at which proton-proton collisions occur between the two counter-rotating beams of the LHC. At each end of the detector magnets focus the beams into the interaction point. At collision each beam has a radius of 17 μm and the crossing angle between the beams is 285 μrad. At full design luminosity each of the two LHC beams will contain 2,808 bunches of 1.15×1011 protons. The interval between crossings is 25 ns, although the number of collisions per second is only 31.6 million due to gaps in the beam as injector magnets are activated and deactivated. At full luminosity each collision will produce an average of 20 proton-proton interactions. The collisions occur at a centre of mass energy of 8 TeV. But, it is worth noting that for studies of physics at the electroweak scale, the scattering events are initiated by a single quark or gluon from each proton, and so the actual energy involved in each collision will be lower as the total centre of mass energy is shared by these quarks and gluons (determined by the parton distribution functions). The first test which ran in September 2008 was expected to operate at a lower collision energy of 10 TeV but this was prevented by the 19 September 2008 shutdown. When at this target level, the LHC will have a significantly reduced luminosity, due to both fewer proton bunches in each beam and fewer protons per bunch. The reduced bunch frequency does allow the crossing angle to be reduced to zero however, as bunches are far enough spaced to prevent secondary collisions in the experimental beampipe.